3736 results

  • Oblique wave attack on rubble mound breakwater crest walls of finite length

    Authors: Mares-Nasarre, P.; Gent, M.R.A. van (2020)
    Published in: Water, volume 12 (2020) issue 2, page 1-10

    Rubble mound breakwaters usually present a crest wall to increase the crest freeboards without a large increase of the consumption of material. Methods in the literature to design crest walls are based on estimates of the wave loads. These methods are focused on the maximum loading that attacks a single position of the crest wall. In practice, crest walls have a finite length. Since the maximum loading does not occur at the same instant over the entire length of the crest wall for oblique waves, these methods overestimate the loading in the situation of oblique waves. Wave loads under oblique wave attack have been measured in physical model tests. A method to account for the effect of the finite length of crest walls has been developed, and design guidelines have been derived. The results of this study in combination with the existing methods in the literature to estimate the wave forces enable a more advanced design of crest walls.

  • Evaluation and improvement of remote sensing-based methods for river flow management

    Authors: Samboko, H.T.; Luxemburg, W.M.J.; Savenije, H.H.G.; Makurira, H.; Banda, K.; Winsemius, H.C. (2020)

    Rapid advancements in technologies open up possibilities for water resource authorities to increase their ability to accurately, safely and efficiently establish river flow observation through remote and non-intrusive observation methods. Low-cost Unmanned Aerial Vehicles (UAVS) in combination with Global Navigation Satellite Systems (GNSS) can be used to collect geometrical information of the riverbed and floodplain. Such information, in combination with hydraulic modelling tools, can be used to establish physically based relationships between river flows and permanent proxy. This study proposes a framework for monitoring volatile, dangerous and difficult to access rivers using only affordable and easy to maintain new technologies. The framework consists of four main components: i) establishment of geometry using airborne photogrammetry and bathymetry; ii) physically based rating curve development through hydraulic modelling of surveyed river sections; iii) determination of non-intrusive observations with for instance simple cameras or satellite observations; and iv) evaluating the institutional and societal impacts of using new technology. To establish this framework, a number of research questions require addressing. First, the factors impacting on accuracy of geometrical information of the floodplain terrain and bathymetry need to be investigated. Second the accuracy of a physically based rating curve compared to a traditional rating curve needs to be established. Third, for rapidly changing river segments, it should be investigated if the collection of occasional snapshots of multiple proxies for flow can be used to assess the uncertainty of river flows. The study finally explores the social and institutional impact of using new technologies for remote river monitoring. If these research gaps are addressed, this may strengthen water manager's ability to observe flows and extend observation networks.

  • Sediment disposals in estuarine channels alter the eco-morphology of intertidal flats

    Authors: Vet, P.L.M. de; Prooijen, B.C. van; Colosimo, I.; Ysebaert, T.; Herman, P.M.J.; Wang, Z.B. (2020)
    Published in: Journal of geophysical research : earth surface (2020), page 1-37

    Dredging of navigation channels in estuaries affects estuarine morphology and ecosystems. In the Western Scheldt, a two‐channel estuary in the Netherlands, the navigation channel is deepened and the sediment is relocated to other parts of the estuary. We analyzed the response of an intertidal flat to sediment disposals in its adjacent channel. Decades of high‐frequency monitoring data from the intertidal flat show a shift from erosion toward accretion and reveal a sequence of cascading eco‐morphological consequences. We document significant morphological changes not only at the disposal sites, but also at the nearby intertidal flats. Disposals influence channel bank migration, driving changes in the evolution of the intertidal flat hydrodynamics, morphology, and grain sizes. The analyzed disposals related to an expansion of the channel bank, an increase in bed level of the intertidal flat, a decrease in flow velocities on this higher elevated flat, and locally a decrease in grain sizes. These changes in turn affect intertidal flat benthic communities (increased in quantity in this case) and the evolution of the adjacent salt marsh (retreated less or even expanded in this case). The shifts in evolution may occur years after dredged disposal begins, especially in zones of the flats farther away from the disposal locations. The consequences of sediment disposals that we identify stress the urgency of managing such interventions with integrated strategies on a system scale.

  • Validatie effectmodule landbouw

    Authors: Briene, M.; Kooij, S. van der; Swart, L. de; Snippen, E.; Vat, M.P. van der; Schasfoort, F.E.; Mens, M.J.P. (2019)

    In deze validatiestudie vergelijken we de uitkomsten van de Effectmodule Landbouw met meetgegevens over de gevolgen van droogte in 2018 op de landbouwsector. Voor de validatie zijn twee simulaties in het Landelijk Hydrologische Model (LHM) uitgevoerd van het jaar 2018. De uitkomsten van de validatie zijn bedoeld voor het opstellen van concrete aanbevelingen voor de Effectmodule die op korte termijn geïmplementeerd kunnen worden zodat deze mogelijk meegenomen kunnen worden in de economische analyse voor het Deltaprogramma Zoetwater. Daarnaast worden aanbevelingen opgesteld voor structurele verbeteringen van de Effectmodule voor een bredere toepassing dan alleen het Deltaprogramma Zoetwater. Aanbevelingen voor operationele toepassing in het waterbeheer vallen buiten de scope van deze opdracht.

  • Validatie effectmodule scheepvaart

    Authors: Briene, M.; Kooij, S. van der; Swart, L. de; Snippen, E.; Wijk, R.M. van der; Schasfoort, F.E.; Mens, M.J.P. (2019)

    In de voorliggende studie worden de resultaten van het Binnenvaart Analyse Systeem (BIVAS) en de Effectenmodule Scheepvaart vergeleken met waarnemingen voor het droge jaar 2018. De uitkomsten van deze validatie zijn bedoeld voor het opstellen van concrete aanbevelingen voor de Effectmodule die op korte termijn geïmplementeerd kunnen worden zodat deze mogelijk meegenomen kunnen worden in de analyses van het Deltaprogramma Zoetwater. Daarnaast worden aanbevelingen opgesteld voor structurele verbeteringen van de Effectmodule voor een bredere toepassing dan alleen het Deltaprogramma Zoetwater. Aanbevelingen voor operationele toepassing in het waterbeheer vallen buiten de scope van deze opdracht.

  • Data-analyse Kierproef Haringvliet ZS2019_2 Zoetspoelen (12-2-2019 -12-3-2019)

    Authors: Tiessen, M.C.H.; Kranenburg, W.M. (2019)

    Dit document beschrijft de opzet, resultaten en analyse van Kierproef ZS2019_2. Dit is de tweede zoetspoelproef uitgevoerd in het kader van het “Lerend Implementeren” van het Kierbesluit. In opzet is de proef vergelijkbaar met de eerste zoetspoelproef, alleen zijn er tijdens deze proef andere condities opgetreden. De proef heeft plaatsgevonden tussen 12 en 21 februari 2019. De data-analyse omvat de periode 12 februari t/m 12 maart 2019.

  • Development of a sixth generation model for the NW European Shelf (DCSM-FM 0.5nm) : model setup, calibration and validation

    Authors: Zijl, F.; Groenenboom, J. (2019)

    Upon request of Rijkswaterstaat (RWS) Deltares has developed a sixth-generation hydrodynamic model of the Northwest European Shelf. Specifically, this model covers the North Sea and adjacent shallow seas and estuaries in the Netherlands, such as the Wadden Sea, the Ems-Dollard estuary, the Western Scheldt and the Eastern Scheldt. The development of this model (DCSM-FM) is part of a more comprehensive project in which sixth-generation models are developed for all waters managed and maintained by RWS. An important difference with the previous fifth generation models is the use of the D-HYDRO Suite, the new software framework for modelling free surface flows, which was first released in 2015 and allows for the use of unstructured grids. While the previous generation models for the same area were specifically aimed at an optimal representation of water levels for operational forecasting under daily and storm surge conditions, for the sixth-generation model(s) the scope is wider. This model should also be suitable to use for e.g. water quality and ecology studies, oil spill modelling, search and rescue and to provide three-dimensional (3D) boundary conditions (including temperature and salinity) for detailed models of e.g. the Haringvliet and Rhine-Meuse Delta (RMM). The above applications pose a wide range and sometimes mutually exclusive demands on a model. Therefore, two horizontal schematizations were proposed: 1. DCSM-FM 0.5nm: a relatively coarse schematization (minimum grid size of 800-900 m in Dutch waters), primarily aimed at ensemble-based probability forecasting, but also forming a sound basis for a future three-dimensional model development including temperature and salinity as state parameters. 2. DCSM-FM 100m: a relatively fine schematization with a minimum resolution of -100 m in some Dutch waters (such as the Wadden Sea) to be used for accurate (operational) water level forecasting. This model will be a based on the model in item 1a, but with refinement where required. The present report deals with the development of the relatively coarse two-dimensional DCSM-FM model (DCSM-FM 0.5nm).

  • Assessment of impacts of plantation drainage on the Kampar Peninsula peatland, Riau

    Authors: Hooijer, A.; Vernimmen, R.R.E.; Mawdsley, N.; Page, S.; Mulyadi, D.; Visser, M. (2015)

    Indonesia and Malaysia are now the only countries attempting to convert peatlands to agriculture and silviculture at a large scale. The rate of carbon loss, and of associated CO2 emissions and land subsidence, is highly temperature dependent, and therefore proceeds at a faster rate in the tropics than in other climate zones. We demonstrate the rate of peat surface subsidence, increased flood risk and carbon emission for the Kampar Peninsula (KP) in Riau, Indonesia. An elevation model (DTM) was constructed from LiDAR data, and land use was determined from Landsat analyses and plantation concession data from the government. The elevation model was used to create a map of minimum peat thickness and carbon stock for the KP, assuming the base of the peat (i.e. where the underlying mineral soil layer starts) to be at 2 m above Mean Sea Level (MSL). This measure of minimum peat thickness can underestimate actual peat thickness by several metres, as the peat base is actually often around or even below MSL, as explained in this report.

  • Progression rate of backward erosion piping in laboratory experiments and reliability analysis

    Authors: Pol, J.C.; Beek, V.M. van; Kanning, W.; Jonkman, S.N. (2019)
    Published in: Proceedings of the 7th International Symposium on Geotechnical Safety and Risk - ISGSR 2019 (Taipei, Taiwan, 12-13 December 2019) (2019), page 1-6

    This paper analyses the average pipe progression rates in 45 backward erosion piping experiments from six datasets. A large variety of test configurations is covered, creating a larger range in outcomes as the erosion process is affected by the type of setup. The progression rates vary from 5.10-5 to 2.10-3 m/s, and can be predicted reasonably well by the (critical) hydraulic gradient and the hydraulic conductivity. As can be expected because of scale effects, the lowest values are found in the full scale tests. Therefore, the lower values are expected to be more representative for field conditions. Due to the considerable uncertainty in the predictive formulas, care should be taken in the application of these to situations outside the range of the experiments. Secondly, it is shown how these progression rates can be included in a reliability analysis of backward erosion in dikes. For this purpose a Monte Carlo framework was adopted/developed that includes multiple time-dependent limit state functions. Application of this framework to five hypothetical cases shows the possible contribution to dike safety of the inclusion of the pipe growth process. The chosen flood durations are two extremes for water systems in the Netherlands: a relatively long riverine (Rhine) flood wave and a short coastal storm surge. Effects on the failure probability are small for the riverine cases (factor 1-2), but much larger for the coastal cases (factor 3-104). In the riverine area, there is still a significant delay in the expected time of failure of several days, which is beneficial for emergency response. Future work should further explain the differences in the found progression rates, the underlying mechanism and scale effects. Subsequently, the reliability analysis should be extended and applied to more dike sections, to assess the potential of including these aspects in safety assessments and emergency strategies. More research is also needed into the effect of a partly developed pipe that is already present at the start of a flood event.

  • Sandy strategies for resilience : lessons learned from BWN

    Authors: Eekelen, E. van; Luijendijk, A.P.; Ouwerkerk, S.; Steetzel, H.J.; Penning, W.E. (2019)
    Published in: Hydrolink (2019) issue 4, page 106-109

    Amongst the various Nature-Based Solutions (NBS) for flood defenses, sandy strategies are well-known and applied regularly in sandy coastline systems to counter or compensate erosion. However, this is only part of the possibilities that sandy strategies offer as they provide additional benefits by bringing new habitats and supporting biodiversity and recreational areas through the active development of ecosystems ranging from new dunes to foreshores. Several sandy strategies have been piloted in the Netherlands by the EcoShape consortium, a Dutch consortium on NBS knowledge development termed Building with Nature (BWN), in order to establish a knowledge base regarding the full palette of opportunities for sandy strategies. It was found that although the studied cases operate very differently and have inherent differences in supplying and using (ecosystem) functions, and that their feasibility is strengthened by the availability of sand and an appreciation for the strategy's long term flexibility and contribution to (coastal) resilience.

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